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Postmining Topography, and designs are discussed in further detail in Tab 20, Backfilling • <br />and Grading and Tab 17, Probable Hydrologic Consequences. Seeding the topsoil stockpiles <br />with an annual grain cover crop or native grasses and fortis, including vigorous rooting <br />and nitrogen fixing plants such as alfalfa, will be done to prevent erosion and also <br />improve the fertility and physical filth of the soil. The seed mixture, seeding method, <br />and seeding rate for topsoil stockpiles is described in the Revegetetion Plan, Tab 22, <br />Table 22-6, the Seed Mixes and Plant Material Lists section of Tab 22, and the Topsoil <br />Storage section of this tab. The topsoil removal area at any one time shall be minimized <br />to prevent both wind end water erosion. <br />Peabody does not propose to use any selected overburden materials es topsoil substitutes <br />or plant seedbed media. This is based on results of the soil survey and topsoil inventory <br />for Seneca fI-Y. sufficient quantities of suitable quality topsoil are available to <br />restore the disturbed areas to the desired postmine land use. Following mining, an <br />average of 1.3 feet of suitable topsoil will be replaced over the final graded spoil <br />medium. <br />No topsoil will be replaced on those facilities which ere to be retained to compliment the • <br />final postmine lend use. Theae facilities include the high water line area end spillway <br />of Ponds 005 end 006 (5.0 acres), and a 100-foot-wide section of the mine entrance road <br />(19.5 acres), Road A (20.2 acres), Road G (21.8 acres), and Roed H (19.7 acres). <br />Research over the last ten years has demonstrated that topsoil depths required for optimum <br />production are related to the quality of the underlying spoil, with greater depths of good <br />quality soil needed to restore production on poor quality spoil (U.S. Congress, 1986). <br />Poor quality spoil materiel may require- more than three feet of topsoil replacement <br />whereas good quality spoil may need less than one foot. In North Dakota, the replacement <br />of one foot of subsoil plus one foot of topsoil over good quality spoil materials is <br />recommended (Doll et al, 1984). Power et al., (1976) end Berth and Martin (1982) <br />demonstrated that three feet of topsoil was necessary for optimum production on sodic <br />spoil, earth end Martin, 1981, showed fine sandy loam topsoil depths for optimum <br />production in southeastern Montana to be less than one foot for optimum perennial grass <br />production on nonsaline, nonsodic silt loam spoil. Schuman and others (1980) found that <br />native grass production on reclaimed spoil in Yyoming equaled forage production on an <br />undisturbed native area when the topsoil thickness was 1.3 feet. In northwestern • <br />30 Revised OL/24 /91 <br />